The invention relates to a bread maker whose temperature control response is improved.
FIG. 8 is a sectional view showing a construction of a conventional bread maker A. In FIG. 8, reference numeral 1 designates a cylindrical baking oven main body; 2, an operation panel that is arranged in the middle of the front of the baking oven main body 1 for specifying a baking time and a finishing condition; and 3, a dome-like glass cover mounted on top of the baking oven main body 1 so as to be opened and closed. The baking oven main body 1 and the glass cover 3 provide a closed space of the bread maker. The operation panel 2 has a menu select button, a menu set button, a start button, and the like. In this bread maker, the glass cover 3 is constructed of transparent glass so that the inside of the baking oven main body 1 can be seen through with the glass cover 3 closed. The glass cover 3 is rotatably attached to a bracket 4 at the rear end thereof, the bracket 4 being mounted on the baking oven main body 1. The glass cover 3 also has a handle 5 attached to the front end thereof so that the glass cover 3 can be opened and closed. Inside the baking oven main body 1 is a cylindrical inner case 8. Further, an operation board 9 having a display corresponding to the operation panel 2, a keystroke drive section, and the like is arranged. A circuit board 10 for effecting the entire control is also arranged.
An internal temperature sensor 17 and a heat-ray radiation type heater 12 serving as an electrically heating element are secured to the inner circumferential surface of the inner case 8 in annular form. Inside the inner case 8 are a bread baking case 13 and a stirring blade 14. The bread baking case 13 is a cylindrical case whose top is opened. The stirring blade 14 mixes and kneads bread making ingredients including water charged into the bread baking case 13. The stirring blade 14 is rotatably arranged on the bottom of the case 8. Further, a dough sensor 11 for detecting the temperature of the ingredients during the stirring process is attached to the stirring blade 14. A stirring motor 16 is fixed below the baking oven main body 1, so that the stirring blade 14 rotates through pulleys 19a, 19b and a timing belt 20. A projecting rod 15 is attached to the inner wall of the bread baking case 13 lest the dough formed by stirring should rotate together with the stirring blade 14. Reference numeral 25 designates a fan motor; 26, a fan; and 27, a fan heater.
The circuit board 10 has a control circuit 50 for controlling the entire part of the bread maker A. FIG. 9 is a block diagram showing a configuration of the control circuit 50. In FIG. 9, the same or like parts and components as those shown in FIG. 8 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 9, reference numeral 17 designates an internal temperature sensor, whose comparator compares a detected temperature with a fixed heater control reference value. Further, reference numeral 18 designates a microcomputer for effecting system control; 30, a relay for energizing and deenergizing the heater 12; 33, a relay for energizing and deenergizing the fan heater 27; and 31 and 32, relays for energizing and deenergizing the stirring motor 16 and the fan motor 25, respectively. The microcomputer 18 has ROMs and a RAM as a storage area and an I/O port and an A/D converter port as an interface. The ROMs include a ROM 52 that stores a control program related to the execution of the respective bread making processes, and a ROM 53 that stores related data.
Reference numeral 51 designates a power supply circuit of the bread maker A, which not only feeds dc power to the control circuit 10 by converting commercial power supply on the primary side into dc power supply, but also feeds ac power to the heater 12, the fan heater 27, the stirring motor 16, and the fan motor 25.
Next, a temperature control operation of the aforementioned bread maker A will be described. FIG. 10 is a flowchart showing the temperature control operation of the bread maker A. A program indicated by the flowchart is located in process control programs requiring temperature control for such processes as stirring, fermenting, and baking processes of the bread maker A. Therefore, the process control programs requiring temperature control can be executed by the program indicated by the flowchart. According to the flowchart, temperature data inside the bread maker detected by the internal temperature sensor 17 is read (Step S100), and the read temperature data is compared with a reference value corresponding to a desired target temperature Ta (Step S101). As a result, if the read temperature data is judged to be lower than the reference value corresponding to the target temperature Ta, then the heater 12 is turned on to start conduction to the heater 12 (Step S103). On the other hand, if the temperature data read in Step S101 is judged to be higher than the reference value corresponding to the target temperature Ta, then either the heater 12 that has been turned on is turned off to stop conduction to the heater 12 or no conduction is made to the heater 12 (Step S102).
Therefore, in temperature control for heating the bread baking case 13, when the heating of the heater 12 that has been left cold is started to cause the temperature of the bread baking case 13 to be increased by the heater 12, the internal temperature sensor 17 detects such temperature increase, and in response thereto, the microcomputer 18 effects automatic on/off control of the heater 12 so that the temperature of the bread baking case 13 reaches the target temperature Ta as shown in FIG. 11.
As shown in FIG. 11, a sensor curve x shown by the solid line indicates the values detected by the internal temperature sensor 17, whereas a temperature curve y shown by the broken line indicates actual temperatures of the bread. The temperature curve y is initially fluctuating with large overshoot and undershoot but is gradually stabilized with the fluctuations controlled within a predetermined range D. The actual surface temperature of the bread is rather high and is away from the target temperature Ta in the initial part of the temperature curve y in particular as shown in FIG. 11 due to the heat capacity of various parts and components of the bread maker.
As described above, the heater 12 is controlled on the basis of a fixed heater control reference value corresponding to a set target temperature.
The conventional bread maker A is constructed as described above. That is, the heating control of the bread baking case 13 in particular involves the steps of reading the temperature data inside the bread maker detected by the internal temperature sensor 17, and comparing the read temperature data with a fixed reference value corresponding to a target temperature Ta. As a result of such heating control, the temperature fluctuates not only with large overshoot and undershoot at an initial temperature control period but also within a large range even at the steady state as shown in FIG. 11. Therefore, temperature control with satisfactory response and high accuracy within a small fluctuating range has not been achieved.